Synthetic fiber and method of manufacture

ABSTRACT

The present invention relates to a method for producing a synthetic fiber for use in an artificial grass sports field, including the steps of supplying a layer of synthetic material; and obtaining the synthetic fiber from the layer of synthetic material, wherein the layer of synthetic material comprises at least two layers of different synthetic materials, using a co-extrusion process. The invention also relates to such a synthetic fiber and to an artificial lawn suitable for sports fields, including a substrate to which synthetic fibers according to the invention have been attached.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority based on Netherlands Application No. 1026239 filed on May 19, 2004 and is the National Stage of International Application No. PCT/NL2005/000275 filed on Apr. 11, 2005, which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to synthetic fibers and methods for producing synthetic fibers for use in artificial grass sports fields.

BACKGROUND OF THE INVENTION

Currently, synthetic materials are being used for numerous purposes. For example, the use of various sorts of synthetic materials in artificial lawns for sports fields has markedly increased in recent years.

Research in this regard has concentrated on the development of synthetic fibers for use in artificial lawns for sports fields, in which fibers of a particular length are attached to a substrate, for example, by tufting. The development of artificial grass fibers and artificial grass sports fields derived therefrom has progressed to the point that it is now possible to construct artificial grass sports fields which are very difficult to distinguish from natural grass sports fields, not only with regard to the way they look but also, and in particular, with regard to the way they function during play.

Unlike natural grass sports fields, artificial grass sports fields can be played on longer and more intensively, regardless of the weather conditions. Currently, the development of new artificial grass fibers is particularly focused on obtaining a fiber that will further reduce the incidence of injuries such as grazes and burns caused by sliding or twisted joints.

Existing fibers specifically developed for an artificial grass sports field are obtained from a layer of synthetic material, for example, by means of a cutting operation. The layer of synthetic material may consist of a mixture of different synthetic materials, for example, with one synthetic material serving to give the fiber a certain strength (against breaking or splitting), while another synthetic material in the mixture provides the fiber with a certain elasticity or flexibility or better sliding properties.

A drawback of such existing synthetic fibers is the fact that, due to the homogeneous structure all sub-properties of the fiber are homogeneously incorporated in the fiber. As a result, certain properties of the fiber may be less prominently present than is desirable, while other properties predominate more than is desirable. Therefore, the composition of currently available fibers is usually standardized and often their production and material costs are unnecessarily high.

SUMMARY OF THE INVENTION

The present invention provides a method for producing a synthetic fiber for use in an artificial grass sports field, comprising the steps of supplying a layer of synthetic material; and providing or obtaining the synthetic fiber from the layer of synthetic material wherein the layer of synthetic material comprises at least two layers of different synthetic materials using a co-extrusion process.

The invention also provides a synthetic fiber and an artificial lawn suitable for a sports field, including a substrate to which synthetic fibers according to the invention are attached.

Stated another way, the present invention relates to a method of producing a synthetic fiber for use in an artificial grass surface comprising: i) providing a layer of synthetic material comprising at least two layers of different synthetic materials having different function-specific properties; and ii) forming the synthetic fiber therefrom using a co-extrusion process.

Moreover, after step i), the layer of synthetic material can be stretched or, after step ii), the synthetic fiber can be stretched to significantly improve the playing properties of an artificial grass surface including the synthetic fiber.

The present invention provides a more universal fiber, which, on the one hand, can be produced for a specific use and which, on the other hand, saves production and material costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D show different embodiments of a synthetic fiber according to the present invention; and

FIGS. 2A and 2B schematically show a few embodiments of an artificial grass sports field provided with a synthetic fiber obtained by using the method according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention disclosed herein is, of course, susceptible to embodiment in many forms. Shown in the drawings and described herein in detail are preferred embodiments of the invention. It is understood, however, that the present disclosure is an exemplification of the principles of the invention and does not limit the invention to the illustrated embodiments.

As will be seen herein, the present invention provides a more universal fiber which, on the one hand, can be produced for a specific use and which, on the other hand, saves production and material costs. According to the invention, the layer of synthetic material comprises at least two layers of different synthetic materials, using a co-extrusion process.

The co-extrusion process accomplishes a separation of the various properties of the synthetic materials that are used. By providing the synthetic fiber with a layered structure, it becomes possible to provide each layer with a function-specific property, which property does not need to be present elsewhere in the fiber, or needs to be present only to a markedly reduced degree. This makes it possible to select the formulation for the fiber specifically for a certain use, which, in addition to a more efficient material consumption, also results in a synthetic fiber with markedly improved playing and fiber properties than in the case of homogeneously composed known fibers.

According to the present invention, the playing properties of the synthetic fiber are significantly improved by stretching the fiber after the co-extrusion process. Apart from an increase in length, according to the invention, the selection of materials is important so that after the stretching process a fiber is provided with such strength properties in a transverse direction that the fiber will split less easily, for example. When used in an artificial grass sports field, such a fiber, and consequently the artificial lawn, has a much longer life, and the artificial lawn requires much less maintenance, thus remaining playable longer. Furthermore, the risk of injury to a player is considerably reduced.

According to the invention, the fiber can comprise at least one monofilament or several twined monofilaments. The fiber can be formed as a band, and more in particular the band fiber can be formed as a fibrillated band fiber.

In a first functional embodiment of the process according to the present invention, the layer of synthetic material comprises a core layer of a first synthetic material having two sides, which core layer is surrounded on both sides by one or several outer layers, each consisting of a different synthetic material.

Thus, a functional separation of the different properties of the different synthetic materials is achieved, in which each layer of synthetic material has a function-specific property, which is not necessary or not functional elsewhere in the fiber.

The layers can have different thicknesses, depending on the desired function-specific properties of the synthetic fiber to be obtained.

In a first embodiment, the first synthetic material comprises a mixture of a polymer and a plastomer, in which preferably the ratio of the plastomer in the core layer is about 30 to about 80 weight percent and more preferably the ratio of the plastomer in the core layer is about 30 to about 50 weight percent. This results in a fiber having a core layer which, from a function-specific viewpoint, exhibits a very favorable non-splitting behavior.

In another embodiment, at least one of the other synthetic materials includes a hydrophilic additive. The artificial grass fiber thus obtained has the function-specific characteristic that it can absorb moisture (water). This keeps the artificial grass sports field moist longer, which has a positive effect on playing behavior (slides etc.). When the field is played on, the absorbed moisture is released, the same as with natural grass.

An example of a hydrophilic additive that can be used as the top layer or outer layer of the co-extrusion fiber is ethylene vinyl alcohol copolymer. Depending on the quantity of vinyl alcohol in the copolymer, this polymer is capable of absorbing a considerable amount of water.

Another embodiment of a hydrophilic additive is polyhydroxyethyl methylacrylate.

In yet another embodiment, at least one of the other synthetic materials can comprise an antistatic additive. As a result, any static electricity generated when the field is played on can discharge. Usually, the material spread or strewn between the fibers, which is used in many artificial grass sports fields, is statically charged during play and as a result migrates upwards in the field. Thus, the granular strewing material can be spread through the air, which is less pleasant during play.

The antistatic additive also ensures that no static discharges will take place via the players.

More specifically, the antistatic additive can be a polymer, especially a permanent antistatic agent, such as a polyamide or a polyether block amide. In another embodiment, the additive is a polyester block copolymer.

The invention will now be explained in more detail with reference to the drawings, in which:

FIGS. 1A-1D show different embodiments of a synthetic fiber according to the present invention; and

FIGS. 2A and 2B schematically show a few embodiments of an artificial grass sports field provided with a synthetic fiber obtained by using the method according to the present invention.

The fibers (10, 20, 30, 40) are obtained from a foil of a synthetic material, which foil, obtained by co-extrusion, comprises at least two layers of different synthetic materials (11, 12) as shown in FIG. 1A. Contrary to the currently known synthetic fibers, which comprise a homogeneous mixture of synthetic materials, the layered structure of the synthetic fiber (10, 20, 30, 40) according to the present invention makes it possible to provide each layer (sub-layers 11 and 12 in this embodiment) with a function-specific property. As a result, the use of a synthetic material having a specific property in a particular part of the synthetic fiber obviates or strongly reduces the need for the presence of this synthetic material and the related function-specific property elsewhere in the fiber.

For example, it is possible to use a synthetic material for the sub-layer 11 which provides the synthetic fiber with the required mechanical strength (and rigidity) and, in particular, non-splitting properties such that the synthetic fiber used for the artificial grass sports field will not split as a result of being played on.

In another embodiment as shown in FIG. 1B, the synthetic fiber 20 is built up of three layers of three different synthetic materials indicated by reference numerals 21, 22, 23. The middle layer 21 is made of an inexpensive synthetic material that gives the fiber 20 its mechanical strength, while the outer layers 22 and 23 are made of different synthetic materials, each of which exhibit a different function-specific property, which property is located best on the outer side of the synthetic fiber rather than in the center.

Thus, the outer layers 21 and 22 can have an elastic property, for example, contrary to the inner layer 21, which provides the fiber with a certain rigidity (against breaking or splitting), which elastic property of the outer layer 21 or 22 has a positive effect on the playing properties of the artificial grass sports field.

Whereas in the embodiment of FIG. 1B the outer layers 22 and 23 can be made of different synthetic materials, FIG. 1C shows an embodiment in which the outer layers 32 a and 32 b are made of the same synthetic material.

FIG. 1D shows a further, more complex layered structure of a synthetic fiber according to the present invention. By means of co-extrusion of different synthetic materials, a layered synthetic fiber made up of a central core 41 and surrounded by different types of outer layers 42 a-42 b or 43 a-43 b, respectively, is obtained.

The essence of the method according to the invention and the synthetic fibers according to the invention obtained thereby lie in the fact that the synthetic fiber, contrary to the known synthetic fibers, does not have a homogeneous structure in which all different synthetic materials and the related properties are homogeneously incorporated in the fiber. As a result of the homogeneous structure or composition of the existing artificial grass sports fields, certain properties of the fiber may be present less prominently than is desirable, whereas other properties are more predominantly present than desired.

Using the method according to the invention, it is possible to obtain synthetic fibers according to a specific formulation that, contrary to standardized fibers, exhibit a function-specific property in certain parts of the fiber that is not considered necessary or desirable elsewhere in the fiber.

This enables a more efficient use of the various (synthetic) materials, which not only serves to reduce costs but also provides a more universal synthetic fiber according to the invention having markedly improved playing and fiber properties than in the homogeneously constructed known fibers. In this specific embodiment, the inner layers 11, 21, 31 and 41 are made of a more inexpensive synthetic material that in principle provides the fiber with a certain strength against breaking or splitting. The outer layers 12, 22, 32, 32 a-32 b, 42 a-42 b and 43 a-43 b are made of a synthetic material that does not necessarily need to be present in the fiber core.

In this context, a specific embodiment can have an outer layer including an antistatic additive. The antistatic additive prevents the fiber from being charged by means of static electricity generated as a result of the artificial grass sports field being played on. On the other hand, the antistatic additive precisely ensures that the generated static electricity can discharge from the artificial grass sports field and, for example, will not discharge via the players, which can lead to unpleasant experiences.

In addition, in most artificial grass sports fields a strewing material (usually made of a rubber-like material) is used, which, due to the static electricity that is generated, migrates upward in the artificial grass sports field and which is spread through the air as a result of the field being played on. The airborne strewing material has a disturbing effect on the players.

The antistatic additive in particular comprises a permanent antistatic agent, for example, a polymer, such as a polyamide or polyether block amide. In another embodiment, the additive is a polyester block copolymer.

In another embodiment, one of the outer layers (or both outer layers) (12, 22-23, 32 a-32 b, 43 a-43 b) can comprise a hydrophilic additive. The artificial grass fiber thus obtained has the function-specific characteristic that it can absorb moisture (water) from the atmosphere, such as rain. This allows the artificial grass sports field to remain moist longer, just like a natural-lawn sports field, which has a positive effect on the playing behavior in particular when sliding, etc. While the field is being played on, the absorbed moisture is released, the same as with natural grass.

An example of a hydrophilic additive that can be used as the top layer or outer layer (12, 22-23, 32 a-32 b, 43 a-43 b) of the co-extrusion fiber is ethylene vinyl alcohol copolymer. Depending on the quantity of vinyl alcohol in the copolymer, this copolymer can absorb a significant amount of water.

The middle layer (11, 21, 31, 41) in this example gives the fiber its strength, while the relatively thin top layer (12, 22-23, 32 a-32 b, 43 a-43 b) absorbs water. This water can be absorbed from the air (in the form of rain, fog, etc.) or can be supplied by an active sprinkler installation. (Often, artificial grass sports fields are sprinkled just before they are played on.)

During play, the absorbed water is released again, which reduces the risk of injury, for example when sliding. Furthermore, the absorbed water keeps the temperature of the field lower, since an artificial grass sports field can be heated by the sun, under adverse conditions to temperatures as high as 70° C.

Another embodiment of a hydrophilic additive as the outer layer (12, 22-23, 32 a-32 b, 43 a-43 b) uses polyhydroxyethyl methacrylate. In order to prevent bonding problems to the middle layer (11, 21, 31, 41), a five-layer co-extrusion configuration is required, as shown in FIG. 1D. The layers 32 a-32 b are bonding layers for the hydrophilic layer 43 a-43 b to the central layer 41 in that case.

For illustration purposes, the various layers of the artificial grass fiber (as shown in FIGS. 1A-1D) are shown having different thicknesses. The thicknesses as shown, however, are illustrative and do not correspond to the actual thicknesses of the produced artificial grass fibers.

In the embodiment shown in FIG. 1D, the bonding layer 42 a-42 b is considerably thinner than shown, usually about 1-5% of the total fiber thickness, while the other layers 41-43 a-43 b are considerably thicker. If polyethylene is used as the middle layer 11-21-31-41, ethylene vinyl alcohol copolymer functioning as the hydrophilic additive will bond to the middle layer without any filling bonding layers being used.

FIGS. 2A and 2B show a few embodiments of an artificial grass sports field in which a synthetic fiber according to the present invention can be applied. In both figures, the artificial grass sports field comprises a substrate 1, to which several synthetic fibers 2 as obtained by using the method according to the present invention are attached at the locations indicated by reference numeral 3, for example by tufting. The synthetic fiber 2 is obtained from a layer of synthetic material, which material is produced from at least two different synthetic materials by means of a co-extrusion process. The synthetic fiber can be individually attached to the substrate or as a bundle of, for example, intertwined fibers 2 a-2 c. More in particular, the fiber that is obtained by co-extrusion can be a fibrillated band fiber.

In another embodiment, as shown in FIG. 2B, the synthetic fiber according to the invention is a monofilament. Also in this case, several monofilaments can be twined to form a bundle, after which each bundle is attached to the substrate 1. In FIG. 2B, the substrate has an open structure and comprises a grid of supporting yarns 1 a-1 b, to which the synthetic fibers 2 are attached.

The foregoing description and the accompanying drawings are illustrative of the present invention. Still other variations in arrangements of materials and components are possible without departing from the spirit and scope of this invention. 

1. A method for producing a synthetic fiber for use in an artificial grass sports field, comprising the steps of: i) supplying a layer of synthetic material; and ii) providing the synthetic fiber from the layer of synthetic material, wherein the layer of synthetic material comprises at least two layers of different synthetic materials, using a co-extrusion process. 2-21. (canceled)
 22. The method according to claim 1, wherein after step i), the layer of synthetic material is stretched.
 23. The method according to claim 1, wherein after step ii), the layer of synthetic material is stretched.
 24. The method according to claim 1, wherein the fiber comprises at least one monofilament.
 25. The method according to claim 24, wherein the fiber comprises several twined monofilaments.
 26. The method according to claim 1, wherein the fiber is in the form of a band.
 27. The method according to claim 26, wherein the band is a fibrillated band fiber.
 28. The method according to claim 1, wherein the layer of synthetic material comprises a core layer of a first synthetic material, which core layer is surrounded on both sides by one or more outer layers, each consisting of a different synthetic material.
 29. The method according to claim 28, wherein the layers have different thicknesses.
 30. The method according to claim 28, wherein the first synthetic material comprises a mixture of a polymer and a plastomer.
 31. The method according to claim 30, wherein the ratio of the plastomer in the core layer is about 30 to about 80 weight percent.
 32. The method according to claim 31, wherein the ratio of the plastomer in the core layer is about 35 to about 50 weight percent.
 33. The method according to claim 28, wherein at least one of the other synthetic materials comprises a hydrophilic additive.
 34. The method according to claim 33, wherein the hydrophilic additive is an ethylene vinyl alcohol co-polymer.
 35. The method according to claim 33, wherein the hydrophilic additive is a polyhydroxyethyl methacrylate.
 36. The method according to claim 28, wherein at least one of the other synthetic materials comprises an antistatic additive.
 37. The method according to claim 36, wherein the antistatic additive is a polymer, in particular a polyamide or a polyether block amide.
 38. A synthetic fiber produced according to the method of claim 1
 39. An artificial lawn suitable for sports fields including synthetic fibers produced according to the method of claim
 1. 40. The artificial lawn according to claim 39, wherein the lawn includes a substrate to which the synthetic fibers are attached.
 41. The artificial lawn according to claim 39, including a granular material between the synthetic fibers.
 42. A method of producing a synthetic fiber for use in an artificial grass surface comprising: i) providing a layer of synthetic material comprising at least two layers of different synthetic materials having different function-specific properties; and ii) forming the synthetic fiber therefrom using a co-extrusion process.
 43. The method according to claim 42, wherein after step 1), the layer of synthetic material is stretched.
 44. The method according to claim 42, wherein after step ii), the synthetic fiber is stretched. 